We demonstrate the 3%mol ytterbium doped phosphate glass air-clad photonic crystal fibre (PCF) laser of 43 cm length in single-mode operation. The fabrication and testing of the fibre laser is introduced. The laser generates from the 12 mum core of photonic microstructure at wavelength of 1030 nm. Near 4-W output power and 14.6% slope efficiency against the launched pump power is demonstrated in preliminary characterization.